Contact spark suppression circuit



Aug. 26, 1952 A. WHARTON ETAL CONTACT SPARK SUPPRESSION CIRCUIT Filed Nov. 28, 1950 LINE HOLD PULSE RELAY RELAY STEP RELAY MAGNET E 2/;

l 3 EA I w EHI l E R l j c RELEASE 1 M I CCT.

--- FIG.I

PULSE GENERATING 1 STEP RELAY MAGNET l2 I l J -KW J FIG'. 2

INVENTORS. THEODOR FRANKEL Patented Aug. 26, 1952 CONTACT SPARK SUPPRESSION CIRCUIT Armistead Wharton and Theodor Frankel, Rochester, N. Y., 'assignors to Stromberg-Carlson Company, a corporation of New York Application November 28, 1950, Serial No. 197,972

This invention relates to electrical control circuits and it more particularly pertains to a spark absorbing or suppression circuit arrangement for contacts used in the control of electrical circuits.

The main object of the invention is to provide simply,'accurately and economically a spark absorbing or suppressing circuit arrangement for the pulsing contacts of the relays used for intermittently controlling highly inductive stepping magnet circuits.

A particular application of the invention is the absorbing or suppressing of the spark at the pulsing'contact's of the pulsing relay, said contacts controlling the intermittent energization of the stepping magnet-of an automatic switch used in control circuits of an automatic telephone system; The pulsing relay intermittently operates in response to impulses transmitted to this relay from a calling station.

Another application of the invention is the suppression of the spark at the pulsing contacts of the pulse generating relay in an allotter, said contacts controlling the stepping magnet of an allotted finder in an automatic telephone system.

' Other objects, applications and advantages not mentioned are realized by means of the particular contact, resistorand capacitor combination disclosed in the accompanying drawing.

"Fig. 1 of the drawing discloses the spark suppression arrangement of the present invention applied to the pulsing contacts of the'pu'lsing relay used for intermittently energizing the stepping magnet of 'a switch in an automatic telephone system.

Fig. 2 of the drawing discloses the spark suppression arrangement of the present invention applied to the contacts of the pulse generating relay which is frequently used in the common allotter for driving the allotted finder in search of the callingline in an automatic telephone system.

The circuit arrangement of this disclosure is quite different from previous spark suppressor circuits, where a non-inductive resistance, in series with a condenser, is connected across the contact or across the magnet winding. In the previous arrangement, the resistor is provided to limit the condenser discharge current to a safe value and in using this scheme, the resistor in series with the condenser reduces the time in which the energy stored in the highly inductive magnetic circuit is absorbed and thus the effectiveness of the condenser in absorbing the spark is reduced from that which would be realized if 2 Claims. (Cl. 175-294) the resistor could be removed from the circuit at the time the spark is to be absorbed. This is what applicants have accomplished in the particular circuit arrangement disclosed in this invention.

Referring to the drawing, contact #I on the pulse relay (or the pulse enerating relay) isof the make-before-break type, with the back or normally closed contact having no circuit connection. This arrangement is much better for adjustment purposes than the familiar single make contact, Where it is required that contact #i make before contact #2 makes when the relay is, operated. With the illustrated arrangemerit, the stop spring 3 (l3 in Fig. 2) may easily be adjusted so that contact #I makes before contact #2 makes, when the relay operates, and thetime during which contact #I is closed beforecontact #2 closes may be easily varied to get the best results for the values of the various circuit elements used.

In, describing the operation of the circuits, it willbe assumed that, in response to a call initiated at a calling substation (not shown),.the

' line relay shown in Fig. 1 is energized over the calling line in the well known manner. The operation of the line relay closes a circuit for operating the hold relay, this circuit extending from ground, make contact of the line relay and winding of the hold relay to battery. The hold relay controls, various circuits, such as the make busy and hold circuits (not shown), as well as preparing the circuit to the pulse relay and the opening up of the circuit to the release magnet of the switch.

It will be obvious that the spark absorbing cir-.

cuit may be applied to a selector or connector notusing the pulse relay, for example, one where the #l and #2 contacts are break contacts on the line; relay, operating in the same sequence asshown for the pulse relay, for controlling the circuitsto resistor R, condenser C and the stepping magnet by way of make contacts of the hold relay.

During the transmission of the impulses from the calling dial, the line relay is intermittently released, once for each impulse, after which it remains operated. During each release of the line relay, the hold relay is de-energized but it is not released because of its slow acting characteristics.

Each release of the line relay closes a circuit for operating the pulse relay, this circuit extending from ground through the break contact of the line relay, make contact of the hold relay and winding of the pulse relay to battery. Consequently, the pulse relay is operated at each release of the line relay and is released at each operation of the line relay during the impulse transmission from the calling dial.

Before the operation of the pulse relay, condenser C is normally charged to the potential of the battery over a circuit extending from ground, condenser C and winding of the stepping magnet to battery. Thus, during the normal condition of the circuit, condenser C is charged to the value of the potential of the exchange battery.

The operation of the pulse relay closes its #1- contact before its #2 contact is closed. When contact #I of the pulse relay is closed, condenser C is first discharged through non-inductive resistor R at a relatively slow rate over a circuit which may be traced from ground through condenser C, resistor R. and contact #I to ground. When contact #2 closes, resistor R. is short circuited through contact #2, and the condenser is short circuited, the upper side of condenser C being grounded through contact #2 and contact #I. This sequential closure of contacts #1 and #2 is efiective to suppress the are due to the condenser discharge because the condenser is first, slowly and partly discharged and then fully discharged when it is short circuited. Direct ground is .now applied to the stepping magnet over a circuit which may be traced from ground, make contacts #1 .and #2 in series and winding of the stepping magnet to battery. Since the stepping magnet is energized from the source of current illustrated, at each operation of the pulse relay, the stepping magnet is intermittently operated to step the automatic switch one step in response to each impulse transmitted from the calling dial.

When the pulse relay releases to de-energize the step magnet, contact #2 opens first. This opens the direct short circuit across thecondenser and, for the moment, leaves it shunted by resistor R. Since resistor R is connected across contact #2, the spark at. this contact will be suppressed and part of the energy stored in the magnetic field of the magnet will be absorbed by condenser C. Now when contact #I opens, the direct current pathis fully opened and the remaining energy stored. in the magnetic field is absorbed by condenser'C. Therefore, the energyabsorbing circuit'is completed in stages by the two-step contact arrangement, thus substantially eliminating the sparl; at the pulsing contacts.

The circuit arrangement of Fig. 2 is similar to Fig. 1, as far as the contact, resistor, condenser and magnet arrangement is concerned. It is contemplated that the spark absorbing arrangement may be used to advantage in connection with a pulse generating relay located in the common allotter for absorbing the spark at'the contacts of the pulse generating relay when this relay is intermittently operated to. generate pulses and transmit them to the stepping magnet of the allotted finder by way of an allotter brush AB, which connects the pulse generating relay of the allotter to the finder. It is not believed necessary to repeat the detailed circuit functions of Fig. 2, since these functions will be evident Irom the corresponding circuit arrangement of Fig. 1.

While the invention has been shown and described as applied to spark absorbing arrangements for use in automatic telephone systems, it should be understood that it is capable of other uses and applications, without departing from the spirit thereof or the scope of the appended claims.

What is claimed isz 1. In an electrical impulsing circuit, a pulse responsive relay having a winding, a circuit for intermittently energizing said winding, said relay having a set of normally open contacts, a resistor connected in series circuit relationship with said contacts and a condenser connected in shunt with said contacts and said resistor, said relay having another set of normally open contacts connected in shunt with said resistor, said another set of contacts being arranged to close a predetermined time later than the closure of the first-mentioned set of contacts in order to short circuit said. resistor and said condenser a predetermined time after the closure of the first men tioned set of contacts when said relayis operated; said another set of contacts also being arranged to open a predetermined time before the opening of the first mentioned set of contacts in order to re-connect said resistor and saidcondenser before said first-mentioned contacts are opened when said relay is dc-energized.

2. In an electrical impulsing circuit, a pulsing relay having a winding, a circuit for intermittently energizing said winding, said relay having two sets of normally open contacts, a stepping magnet, a non-inductive resistor, a" source of direct current, a series circuit comprising said stepping magnet, said non-inductive resistor, one of said sets of contacts, and said source of direct current potential, a condenser in shunt with said resistor and said one set of contacts whereby when said relay is released said capacitor is charged through said stepping magnet, said second set of contacts being adjusted to close a predetermined time-after the closure of said'one setof contacts and-connected in'shunt with said resistor whereby upon the energization of said relay said'first set of contacts completes a first discharge path for said condenser through said resistor and thereafter said second set of contacts short circuits said resistor to complete a second discharge path for said condenser, said second setof contacts also being arranged to open before said first set opens in order to remove the shunt about said resistor to connect said resistor in shunt with said condenser before said first set of contacts opens to disconnect said resistor in order to complete a charging path for said condenser through said stepping magnet.

ARMISTEAD VVI-IARTON. THEODOR FRANKEL.

REFERENCES CITED The following references are of record in the file of this patent:

FOREIGN PATENTS Number Country Date 192,911 Germany Nov. 9, 1907 O'L'lBO England Mar. 29, 1934 

